Technology for automatically detecting a facial region from an image captured by a camera for the purpose of performing facial diagnosis, facial recognition, etc., and technology for automatically detecting a facial region for the purpose of implementing an automatic face tracking function have been developed. For these technologies, methods of detecting skin color have been widely used.
Generally, since the distribution of skin colors varies according to the person and also varies depending on lighting and environmental conditions, it is difficult to accurately extract skin-colored areas from respective input images.
When the range of color values regarded as skin color is wide, skin-colored areas can be extracted regardless of the features of input images. However, in this case, a false alarm or false acceptance causing an area other than a skin-colored area to be erroneously regarded as a skin-colored area may occur. In contrast, when the range of color values regarded as skin color is narrow, false rejection causing an actual skin-colored area to be erroneously regarded as a non-skin-colored area may occur.
Therefore, the modification of a model for extracting an accurate skin-colored area in line with the features of an input image is required.
Conventional technologies related to this modification are described below.
First, Korean Patent No. 2007-0016664 (registered on Feb. 8, 2007) discloses an apparatus and method for generating an RGB map for a skin color model and an apparatus and method for detecting skin color using the RGB map generation apparatus and method. This technology is directed to a scheme for extracting a skin-colored area at high speed using a single fixed skin color model. However, this scheme is disadvantageous in that the accuracy of skin color detection may be deteriorated depending on variation in lighting conditions or the features of an input image.
Korean Patent No. 2007-0008271 (registered on Jan. 17, 2007) discloses another conventional technology directed to a method of detecting and tracking a person in a frontal area in real time and a robot using this method. This technology is also disadvantageous in that, since a person is detected using a single skin color model, the accuracy of skin color detection may be deteriorated depending on lighting or background conditions or the features of an input image.
Korean Patent No. 2006-0012777 (registered on Feb. 9, 2006) discloses a further conventional technology directed to a method of detecting a face using skin color and pattern matching. This technology is configured to detect a skin-colored image using an initially-established skin color model which is established within the range of pixel values detected as pixels of skin color. In this case, when the range of pixel values, detected as skin-color pixels depending on the features of an input image, is narrow, it becomes sensitive to lighting, and thus a problem arises in that false rejection causing an actual skin-colored area to be erroneously regarded as a non-skin-colored area occurs. In contrast, when the range of pixel values is wide, another problem arises in that a false alarm or false acceptance causing a non-skin-colored area to be erroneously regarded as a skin-colored area occurs.
Korean Patent No. 2005-0050061 discloses yet another conventional technology directed to a method of extracting features from a face for inspection. This technology is directed to a scheme for converting an RGB image into a YCbCr image and regarding the YCbCr image as a skin-colored image when the Cb and Cr values of the YCbCr image fall within a specific range. This conventional technology is also configured to detect skin color using a fixed skin color model. In this case, since the fixed skin color model is used as in the above conventional technology, a problem arises in that the accuracy of skin color detection is deteriorated.